The invention relates to a spray pump of the type comprising: a main cylinder in which a pumping chamber is defined; a main plunger slidingly mounted within said main cylinder between a first rest position and a second end-of-stroke position, said plunger being extending by a hollow stem and having a valve seat therein; first resilient means urging said plunger to said first position; a secondary cylinder comprised within said main cylinder; a secondary plunger slidingly mounted in said secondary cylinder between a first closed position and a second open position, said secondary plunger having an upper extension with one end engageable with said valve seat; and second resilient means urging said secondary plunger to said first position, said main plunger being fixedly attached to said secondary cylinder, which determines a space having a closed bottom end and an upper open mouth, through which the pumping chamber and the said space are in communication.
On many occassions during daily life it is necessary to spray liquids of widely varying viscosities onto different surfaces or in different spaces. This need arises, for example, during personal toilet operations for spraying lotions, toilet waters, deodorants or other products on the human body, as well as in domestic cleaning, or for spraying insecticides, air sweeteners, etc.
On such occassions, it is desirable to achieve a powerful spray, not being weak at the start or finish thereof, since otherwise, the spray is preceded by and/or terminated with a weak jet that does not attain the desired objective and is, therefore, wasted and may even cause undesired effects, such as stains, dripping, etc.
Pumps forming a precompression of the product to be dispensed are known and the purpose of such precompression is to allow the vigorous spray mentioned above.
Some of these known pumps have a single spring or resilient means fulfilling two missions, i.e. causing the plunger to return to the starting position once the pump has been operated and providing the desired precompression. These pumps, therefore, have the drawback of not being able separately to control the recovery speed or conditions and the degree of precompression.
In another type of known pumps, of the type described at the beginning, the operation is based on a predetermined relationship between the power of the two resilient means they have, such that one of the springs may not be modified alone, without substantially modifying the operation of the pump or even preventing it from operating.
In these known pumps, since there is no possibility of changing the corresponding springs or resilient means freely and independently, there is a restriction of their field of action, obliging different pumps to be manufactured for different applications, thereby precluding the manufacture of long runs, with the logical adverse effect on costs.
A third group of pumps may be cited which have two springs which may be independently replaced. Nevertheless, these other know pumps suffer from various drawbacks, such as the drawbacks relating to a premature, albeit limited communication of the pumping chamber with the exterior.
In U.S. patent application Ser. No. 07/393.874, commonly assigned, the above drawbacks were overcome, while retaining at all times the advantages derived from the precompression of the product to be dispensed.
The above application did not contemplate any condition concerning the shape of the secondary plunger, whereby it comprises any embodiment thereof.
Nevertheless said secondary plunger was seen in the drawings to have axial cavity, open at both ends, extending along the whole length of the plunger and this feature is claimed in a dependant claim. Furthermore, an embodiment in which said plunger is solid is contemplated.
New research has shown that the fact that the said cavity is open at both ends limits the advantages of the invention as described in said applications, since at the lower portion of the secondary plunger there acts the backpressure generated as a result of the restriction created by the diffusor and the insert, which backpressure is communicated through the plunger cavity and counteracts the inner pressure, which acts to separate the end of the secondary plunger from the valve seat situated within the main plunger. All of this leads to a situation tending to balance the pressures, as a result of which the the pump operation may become difficult and the spraying deficient.